Okay, well this is week four. We're talking about storage and attenuation, the low K zones. This matrix diffusion process, so, Dave, let's go into some more of the key lab and field studies that'll help explain matrix diffusion. >> That sounds good. So remember, our key theme here is that matrix diffusion means storage that contaminants diffusing into these geological media that doesn't really have flowing ground water. That means that contaminants are stored in this media for a really long time. >> So the storage is form of a attenuation but it's not the destructive process but it's more like a process absorption. In the metals world, you can do monitored natural attenuation by the sequestering of metals to this. So it's the same idea that you have some storage this can be an attenuation process. But first, lets go back to sort of put our geology hats on and look at the different geologic media that can sort of a store these contaminants. >> All right, well the NRC back in 2005, they came out with this great document when they sort of tried to divide upsites into these five different type sites that they call them and tried to explain how these might affect how containment is transported. So let's take a look at how these might affect the matrix diffusion processes. So we've got these five right here, and we'll look at them each one in a little bit of detail. >> Got some photos, right? So what's this first one? >> Yeah, the first one might be an example of a Type I media. So this is the Great Sand Dunes National Monument. >> Okay, so more uniform and the idea that Type 1 site at the top left granular media with mild heterogeneity and moderate to high permeability like eolian sands. So Matrix Diffusion in this one? >> Probably not, if it's really just all the same stuff, it's real homogeneous maybe wouldn't see it >> But we have a question mark there because if you remember from last lecture that sometimes those can be at a scale that would be hard to see. And something you think is homogenous may not be, just because of the way that these sands are deposited over time. >> All right, well, that's Type I. If we take a look at the next one, maybe a Type II. This looks something maybe fairly uniform, but probably low permeability, or clay, or something like that, right? >> Exactly, so Type II is they call a granular media. With mild heterogeneity or low permeability, the example is lacustrine clay. So with this, would this have some matrix diffusion effects? >> Sure, not very much invection going on in this type of a median. >> Really being dominated by matrix diffusion. So let's go to number 3. >> Okay, so Type III, we've got a couple use of this one on the left here is an interbedded sandstone and shale, and below there we've got some sort of interbedded sand and silt type situations listed as the Varved Sediments near Searchmont, Ontario. >> Dave, I would like to use geologic terms and in sort of my practice, I'm going to say the word varved sediments once again, if that's okay. >> Yeah, you like to sprinkle those in as you can. >> Exactly. >> Yeah. >> Being a chemical engineer. But what they're talking about here is number three, top right. It says, Granular Media With Moderate to High Heterogeneity. Delta deposits are this key example. Matrix diffusion there? >> Yeah, definitely in those cases. >> Most of our unconsolidated sites are going to be in that type three and you're going to have that matrix diffusion. So the big picture is almost most sites we deal with are going to have some sort of matrix diffusion, and if it's anything like type three, you'll have it. >> Okay. >> Let's go to number four. >> Yeah, number four here we've got a fractured crystalline rock, taken near an observatory in Arizona. >> So this is a hard rock like granite, something like that. It's a fractured media with low matrix porosity. A crystalline rock, so it just depends, the matrix doesn't soak up much of these contaminants but in some cases it is still an important process. So we have a question mark there. >> Yeah. >> Let's go to the last one. >> All right, and this is Door County, Wisconsin. My wife spent a lot of life here as a young person in a cabin on a lake in Door County, but this is real famous for its fractured limestone. >> Okay, so what we have here is this Fractured Media with High Matrix Porosity and it's stuff like limestone, sandstone, fractured clays definitely Matrix Diffusion's the key part right in there. >> Yeah, absolutely. >> Well, let's move down from the geology and sort of thinking about pictures of geology. Let's go to some more tank studies. And so, here is a really nice two layer tank study done by Dr. T. Illangasekare from Colorado School of Mines. This was funded by the US Airforce. But Dave, what's going on in their tank study here? >> Well, like you said, it's two layers. We basically got a fine sand underneath a coarse sand, and then you place this DNAPL source right at the interface. >> Pretty soluble source to trichloroethane, right? >> Yeah, 1, 1, 1 TCA in this case. >> Okay, but let me get this straight. So There's no clays or silts in here, you can have matrix diffusion with just this permeability contrast between a fine sand and a coarse sand? >> Yeah, in this case we're just dealing with sands and let's see what happens when we take a look at the data. >> Okay, so they place the source and they turned it on, let's see the data, let's see what happens. Okay, what's on the axes here? >> So here we're looking at TCA, that's the contaminant they introduced here. So the cumulative TCA is on the y axis and then we have elapsed time in days as they're running this tank study on the x axis. >> Actual milligrams coming out, sort of over time. >> Exactly. >> And this is about a ten day study. Trichloroethane is a pretty soluble component. So they put DNAPL right there that interface and how long will it take to dissolve all that DNAPL away? >> In this case, within five days it had no DNAPL, no TCA DNAPL left. And so, that's sort of your loaning period and then your source's off then after that period. >> I did a field visit to their lab, and they showed me the camera that actually can measure how much of that DNAPL's still in there. And that's the purple squares, right, they're going down. So every day they're taking pictures of this with this x-ray camera. I wanted them to do x-rays to see how my arteries were doing. They said no, it's for DNAPL, we want to see how this works. And after five days, all the DNAPL's gone, and under the sort of a classic evection dispersions type simulation, this thing should have cleaned up on, say, day six, right? >> Yeah. >> But did it? >> No, you're extending out here then into about ten days,right? You see that cumulative mass discharge is still increasing after day five. >> And then I'm looking at the actual green crosses on the bottom. Is that on day six this is the mass itself. In Low Permeability unit. There's a 3000mg. And then day seven, day nine. >> So that's the mass that's been responsible then, for keep you coming off there. >> Yeah, so even just in five days of loading, you had this material almost 4000mg. 4 grams of this TCA diffuse into this Low Permeability unit. Okay, let's keep going on another classic field study. This is from Chapman and Parker Water Resources Research 2005. They got this field site in Connecticut, there's a source zone. And it's flowing ground water sort of flowing under the building here. And then we have Transect 1 as where they done a lot of measurements in here. But a pretty amazing study, right? >> Yeah, a classic study where you've got a lot of fuel data, a lot of modeling data working together to sort of explain what's going on at this site. >> Okay, so let's look at some of the field data. What's going on here in terms of their course? >> Well, this is a case on their left hand, where you've got the distance from the interface. So, 0 is basically the location of that interface, where there's an aquifer on top an aquitard on the bottom. And then you've got on the x-axis, the TCE concentration plotted in this case. And so each one, under those individual points that's shown there, is a concentration measurement from a soil sample that they got out of a core. >> Now, I think it's milligrams per liter. They're sort of doing some conversions, but think about that as the concentration in the core space in that aquitard that silt. And you can see on the right, where you got the sand above that red dashed line, and you got this sort of silty clay underneath it, and you have this mass in there. And they did these calculations to say what's the mass balance, and they come up with, you can see in this slide here, how much mass is underneath there. >> Talking about 3,000 kilograms of TCE present Just in that low-permeability zone that they were investigating. >> And so at this site they completely isolated the denapple source. The sort of denapple source out of circulation but that plume is still being sustained at a lower level of course by this 3000 kilograms, so pretty amazing, the sort of work in there. Now at this site I think they also did some modeling work, what's this graph show? >> Again, we're talking concentration here of TCE, that's basically being shown in these various monitoring wells over time. And so time is there on the x axis, we see 1991 as the start. 1993, they installed an enclosure, right? >> Right. >> And then they waited to see what would happen then to the concentration that they were observing in the monitoring roles. It turns out you didn't see that drop to really low levels that you'd expect based on that sort of dashed purplish blue line right there, what do they see instead? >> So you got this tail line. So the blue is what they were hoping to see once they isolated that source, and concentrations did go down, but maybe one order of magnitude. 90% reduction in concentration, but it just didn't keep going down, it started tailing out, and so with their modeling work they use this to go into their computer modules they said that, they think these matrixes and source might sustain this for hundreds of years. >> Yeah. >> I think is what they came up with them. So now let's wrapt it up for today and we'll talk about some of this lab and field demonstrations, I think Key points here, the matrix diffusion is important in many of our most common hydrogeologic settings. >> Yeah, and again this isn't just something that's been determined by modeling. There's a lot of lab data, a lot of field data sort of backed up that this is an important process. >> Yeah, and some of the key sources out here, the US Air Force, >> AFCAC did some great studies, their Source Initiative papers from Colorado State and Colorado School mines. And then this Chapman and Parker paper is a really good one. And then more recently sort of project 1740, which you and I were part of sort of tells the story of this matrix diffusion process.
